Intermittent inspiratory collapse of the upper airway during sleep. obstructive sleep apnea (OSA), in adults may result in cerebral dysfunction, hypersomnolence and its resultant psychological effects and cardiovascular complications of hypoxemia. (OSA) is known to be more prevalent in the elderly, and this illness likely contributes to the increased occurrence of hypertension, mental dysfunction and stroke in this age group. Anatomical narrowing of the pharynx is often found in younger patients with OSA but is infrequently identified in elderly OSA patients. Therefore, the etiologic mechanisms of upper airway collapse likely are different between elderly and younger patients. It is proposed that physiologic variables are of primary importance in the pathophysiology of OSA in elderly patients. We hypothesize that upper airway inspiratory collapse during sleep in these patients is principally caused by an imbalance between two opposing forces, collapsing and dilating forces, produced by the contraction of chest wall and upper airway inspiratory muscles, respectively. It is further hypothesized that the control systems of these two inspiratory muscle groups are functioning at a level of central neural output where an imbalance of inspiratory activity is present such that upper airway inspiratory collapse results. Therefore, the purposes of this proposal are to: 1) clarify the role of inspiratory muscle activity imbalance in the pathophysiology of OSA in elderly patients, 2) evaluate other potential physiologic variables that may be important and 3) compare the physiologic characteristics of OSA between elderly and younger adult OSA patients. Experiments planned are: A. Periodicity of breathing in OSA. B. Mechanism of imbalance in inspiratory activities of upper airway and chest wall inspiratory muscles. C. Role of increased upper airway compliance in OSA. D. Respiratory system reflexes in OSA. E. Role of muscle fatigue in OSA. Techniques to be used involve the quantitation of electromyogram recordings of upper airway and chest wall inspiratory activity and assessment of upper airway mechanical properties under different experimental conditions during sleep. It is anticipated that the proposed studies will result tn a better understanding of the pathophysiology of OSA in the elderly, and that an effective, safe and simple form of therapy will result from these investigations.